8.1.1  Test codes and practices - part 2

 

Test measurements

(a) Pressure measurement The test pressure measuring system must give the mean static pressure at the condenser inlet from each individual LP turbine cylinder to within ±0.3 mbar, Fig 4.33.

Points of measurement for condenser test

It usually consists of separate sets of pressure sensing holes linked by manifolds to which the test manometers or transducers are connected. The same plane should be used for measuring both the condenser pressure and the turbine LP cylinder exhaust pressure, Fig 4.34.

Plane of pressure measurement for underslung condensers

In addition, the steamside pressure drop should be determined, as this is the most practical means of obtaining the fall in temperature through the tubenest, and also the air extraction pressures.

(b) Temperature measurement Temperatures required are those of CW inlet, CW outlet, condensation outlet, steam and air suction. All are measured directly except that of steam, for which it is preferable to assume saturation and to derive the steam temperature from the corresponding pressure.

The accuracy of the CW inlet temperature measurement equipment is specified as ±0.05°C. Cooling water inlet temperature to the condenser is generally constant across the pipe section and the temperature measurement is made either by a thermometer in a pocket or by extracting a continuous flow of water through a vessel containing a thermometer.

At the entry to the condenser CW outlet pipes, however, the temperature of the water is stratified. To allow mixing to occur, the temperature measurement point is sited as far as possible downstream.

Temperature sampling probes on two diameters are used in each condenser outlet. The probes are either thermopiles or multi-hole probes through which water is drawn into a mixing vessel. The holes or thermocouples are situated at centres of equal areas, one hole or thermocouple to each 0.2 m2 of pipe area.

(c) Flow measurement The flowrates of cooling water, condensate and extracted air may be required when assessing condenser performance. Methods of determining the CW flowrate include:

  • Condenser heat balance.
  • Velocity/area methods.
  • Differential pressure methods.
  • Tracer methods.

These are listed in descending order of preference, and the Site Test Code No. 3 [15] should be consulted for qualifications.

 

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